The statements in this section merely provide background information related to the present teachings and may not constitute prior art.
Ion thrusters are high-efficiency, high-specific impulse, advanced-electric space propulsion systems that are being proposed for ambitious deep-space missions that can require thruster operational lifetimes measured in years. For example, the goal of NASA's Project Prometheus is to advance the future of space exploration by developing Nuclear Electric Propulsion (NEP) technology for deep space missions. Ion thrusters are proposed as the primary propulsion source for such missions and to satisfy the mission requirements must have long life, high-power and high-specific impulse. In these applications, ion thrusters may be required to operate continuously for perhaps as long as 7-14 years.
Commercially available ion thrusters designed for station-keeping and orbit-raising applications can also require extended lifetimes. For example, Aerojet and L3 Communications are designing and developing ion thrusters for integration onto satellites for orbit-raising and station-keeping applications. These ion thrusters have a similar design to NASA thrusters and have the same lifetime limitations and potential failure mechanisms.
One of the primary components of an ion thruster is the discharge cathode assembly (DCA). The DCA can include a hollow cathode with a surrounding keeper and is responsible for initiating and sustaining ion thruster operation. Unfortunately, wear-test and extended-life test results of a 30-cm ion thruster show that a molybdenum (Mo) keeper DCA can last only 3 years due to ion bombardment erosion. Therefore, contemporary Mo keeper DCAs utilized in ion thrusters are incapable of satisfying the 7-14 year mission requirement.
A gas-fed hollow cathode keeper according to the present teachings can reduce ion bombardment erosion by expelling gas through the keeper faceplate. The expelled gas effectively creates a high-pressure “shield” around the keeper such that bombarding ions suffer energy-reducing collisions before impacting the keeper. If the bombarding ion energy is reduced enough, the erosion is eliminated since sputtering is a threshold phenomenon.
Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present teachings.